1. Field of the Invention
The present invention relates to endless structures, in belt or sleeve form, for use in the production of nonwoven products, and more particularly, the instant invention is directed to support members such as belts or sleeves used in the production of patterned, marked, structured or textured nonwoven products.
2. Description of Related Art
The production of nonwoven products is well known in the art. Such products are produced directly from fibers without conventional textile methods such as weaving or knitting operations. Instead, they may be produced by nonwoven manufacturing methods such as airlaid, drylaid, and carding, or some combination of these processes in which fibers are laid down to form an integral nonwoven web.
Nonwoven product may also be produced by airlaying, or carding operations where the web of fibers is consolidated or processed, subsequent to deposition, into a nonwoven product by needling or spunlacing (hydroentanglement.) In the latter, high-pressure water jets are directed vertically down onto the web to entangle the fibers with each other. This process will be discussed in more detail in later parts of this section. In needling, the entanglement is achieved mechanically through the use of a reciprocating bed of barbed needles which force fibers on the surface of the web further thereinto during the entry stroke of the needles.
There presently exists an apparatus for the production of nonwovens, for example, spunbond webs, structures or articles formed from filaments or fibers typically made from a thermoplastic rein. Such an apparatus is disclosed in U.S. Pat. No. 5,814,349, the disclosure of which is incorporated herein by reference. Such apparatuses typically include a spinneret for producing a curtain of strands and a process-air blower for blowing process air onto the curtain of strands for cooling the same to form thermoplastic filaments. The thermoplastic filaments are then typically aerodynamically entrained by the process air for aerodynamic stretching of the thermoplastic filaments, which are then after passing through a diffuser deposited upon a continuously circulating belt or screen (permeable fabric) for collecting the interentangled filaments and forming a web thereon. The web, structure or article, so formed, is then transferred and subject to further processing.
In the meltblown process for manufacturing nonwoven materials, thermoplastic polymer is placed in an extruder and is then passed through a linear die containing about twenty to forty small orifices per inch of die width. Convergent streams of hot air rapidly attenuate the extruded polymer steams to form solidifying filaments. The solidifying filaments are subsequently blown by high velocity air onto a take-up screen or another layer of woven or nonwoven material thus forming a meltblown web.
The spunbonding and meltblowing process can be combined in applications such as spunbound-meltblown-spunbound (“SMS”). In SMS a first layer of spunbonded material is formed on a belt or conveyor. The belt typically has a uniform surface pattern and air permeability to attain the right web formation during the spunbond process. The spunbonded material is deposited on the belt at the lay down forming area to form the web in a first spunbond beam.
A pressure nip, or systems such as utilizing a hot air knife can help to enhance pre-bonding pressure and/or temperature acting on the web. In order to assist in drawing the thermoplastic fibers onto the forming belt, a vacuum box is located beneath the belt and which applies suction to the belt. The airflow needed for the spunbond process is supplied to the system by a vacuum box connected to the appropriately sized vacuum pump.
An airlaid process may also be used to form a nonwoven web. The airlaid process begins with a defibrillation system to open fluff pulp. A conventional fiberizer or other shredding device may also be used to form discrete fibers. Particles of absorbent materials (for example super absorbent powder), abrasives, or other materials may then be mixed with the fibers. The mixture is then suspended in an air stream within a forming system and deposited to a moving forming belt or rotating perforated cylinder onto the circumference of which can be a metallic or polymer sleeve. The randomly oriented airformed fiber may then be bonded by applying a latex binder and drying or thermally bonding.
In general, processes for making nonwoven products have been known for many years. In one process, subsequent to deposition, a fiber batt or web is treated with water streams or jets to cause the fibers to entangle with each other and improve the physical properties, such as strength, of the web. Such techniques for treatment by means of water jets have been known for decades, as may be gathered from the disclosures of U.S. Pat. Nos. 3,214,819, 3,508,308 and 3,485,706.
In general terms, this method involves interlacing of elementary fibers with one another by means of the action of water jets under pressure, which act on the fibrous structure like needles and make it possible to reorient part of the fibers forming the web in the thickness direction.
Such technology has been widely developed at the present time and is used not only for producing what are known as “spunlaced” or “hydro entangled” structures for textile use, such as, in particular for applications in medical fields and hospitals, for wiping, filtration and wrappings for teabags, but also for making tiny perforations in continuous media such as paper, cardboard, films, even sheets of plastic or the like and the articles obtained may be regular and homogeneous, as may be gathered from the disclosure of U.S. Pat. No. 3,508,308, and if required, comprise designs resulting from the reorientation of the fibers, this being essential for an esthetic purpose, as may be gathered from the disclosure of U.S. Pat. No. 3,485,706.
As to products of the “spunlace” or “hydroentangled” type, it has been known for a very long time that the final properties of the product can be adapted by producing mixtures of material, for example by combining a plurality of webs consisting of fibers of different types, for example of natural, artificial or synthetic fibers, or even webs in which the fibers are previously mixed (webs of the “spunbond” type, etc.) with reinforcements that can be incorporated into the nonwoven structure.
French patents FR-A-2 730 246 and 2 734 285, corresponding respectively to U.S. Pat. No. 5,718,022 and U.S. Pat. No. 5,768,756, describe solutions which make it possible to successfully treat hydrophobic fibers or mixtures of these fibers with other hydrophilic fibers or even webs consisting entirely of natural fibers by means of water jets.
In general terms, according to the teachings of these documents, the treatment involves treating a basic web composed of elementary fibers of the same type or of different types, compressing and moistening this basic web and then intermingling the fibers by means of at least one rack of contiguous jets of water under high pressure acting on the basic web.
For this purpose, the basic web is advanced positively on an endless porous support in motion, and it is brought onto the surface of a perforated rotary cylindrical drum, to the interior of which a partial vacuum is applied. The basic web is compressed mechanically between the porous support and the rotary drum which both advance substantially at the same speed. Immediately downstream of the compression zone, a water curtain is directed onto the web and passes successively through the porous support, the compressed basic web and the supporting perforated drum which sucks up the excess water.
The elementary fibers are intermingled continuously, still on the rotary cylindrical drum, by the compressed and wetted web being subjected to the action of at least one rack of jets of water under high pressure. In general, bonding is carried out by means of a plurality of successive racks of water jets which act either on the same face or alternately against the two faces of the web, the pressure within the racks and the velocity of the jets discharged varying from one rack to the next and usually progressively.
It is important to note, as may be gathered from FR 2 734 285, that the perforated roller may comprise randomly distributed micro-perforations. If required, after the initial bonding treatment, the fibrous nonwoven structure may be subjected to a second treatment applied to the reverse face.
In the process of producing spunlaced or hydroentangled nonwoven products, it is desired to impart a pattern or mark on the finished product, thereby creating a desired design on the product. This pattern or mark is typically developed using a secondary process, separate from the nonwoven sheet forming and roll-up process, where a calendar roll is used. These rolls are typically expensive and operate on the principle of compressing certain areas of the fibrous web to create the required patterns or marks. However, there are several drawbacks of using a separate process for creating the pattern or mark on the nonwoven product. For starters, a high initial investment for calendar rolls would be required, which can limit the size of runs that can be economically justified by a producer. Second, higher processing costs would be incurred due to a separate patterning or marking stage. Third, the final product would have a higher than required material content to maintain product caliper after compression in the calendaring step. Lastly, the two-stage process would lead to a low bulk in the finished product due to high pressure compression during calendaring. Prior art nonwoven products made with these known patterning processes do not have clear, well defined raised portions and therefore the desired patterns are difficult to see. In addition, the raised portions of prior art embossed nonwoven products are not dimensionally stable and their raised portions lose their three-dimensional structure when stressed, as for example, when they are handled or laundered.
U.S. Pat. Nos. 5,098,764 and 5,244,711 disclose the use of a support member in a more recent method of producing nonwoven webs or products. The support members have a topographical feature configuration as well as an array of apertures. In this process, a starting web of fiber is positioned on the topographical support member. The support member with the fibrous web thereon is passed under jets of high pressure fluid, typically water. The jets of water cause the fiber to intertwine and entangle with each other in a particular pattern, based on the topographical configuration of the support member.
The pattern of topographical features and apertures in the support member is critical to the structure of the resulting nonwoven product. In addition, the support member must have sufficient structural integrity and strength to support a fibrous web while fluid jets rearrange the fibers and entangle them in their new arrangement to provide a stable fabric. The support member must not under go any substantial distortion under the force of the fluid jets. Also, the support member must have means for removing the relatively large volumes of entangling fluid so as to prevent “flooding” of the fibrous web, which would interfere with effective entangling. Typically, the support member includes drainage apertures which must be of a sufficiently small size to maintain the integrity of the fibrous web and prevent the loss of fiber through the forming surface. In addition, the support member should be substantially free of burrs, hooks or the like irregularities that could interfere with the removal therefrom of the entangled fabric. At the same time, the support member must be such that fibers of the fibrous web being processed thereon are not washed away under the influence of the fluid jets.
One of the main problems which arises during the production of nonwoven products is that of achieving the cohesion of the structure in order to give the products mechanical characteristics according to the application in question, while maintaining or imparting particular physical characteristics, such as bulk, handle, appearance, etc.
The properties of bulk, absorbency, strength, softness, and aesthetic appearance are indeed important for many products when used for their intended purpose. To produce a nonwoven product having these characteristics, a fabric will often be constructed such that the sheet contact surface exhibits topographical variations.
It should be appreciated that these fabrics may take the form of endless loops and function in the manner of conveyors, or as a sleeve mounted on a cylinder. It should further be appreciated that nonwoven production is a continuous process which proceeds at considerable speeds. That is to say, the elementary fibers are continuously deposited onto the forming fabric in the forming section, while a newly manufactured nonwoven web is continuously wound onto rolls after it is dried.